The operation of elevator car and hatchway doors is subject to several conflicting constraints. In the interest of providing efficient elevator service, the doors must open and close in as short a time as practical. In the interest of esthetics, as well as in protecting the mechanical portions of a door operator and associated car and hoistway doors, the doors must operate smoothly and noiselessly without generating undue shock forces in the door operator arms, linkages, and the like. In the interest of safety, the doors must stop quickly when an obstruction is detected in the path of closing doors, with the kinetic energy of the doors and parts rigidly connected thereto being limited by applicable elevator codes.
Closed loop feedback servo control of the elevator doors in which door speed is forced to follow a speed pattern can provide the desired fast, smooth and quiet operation, if the control is properly safeguarded against operation which will unduly stress the control elements mechanically and electrically. The present invention is directed to these protective aspects of elevator door control.